Electrical potential control makes it possible in rotating machines, such as for example generators or high-voltage motors, to minimize electrical voltages (potential differences), thereby allowing the occurrence of partial and/or corona discharges to be reduced or avoided entirely.
In rotating electrical machines, the reliability of the insulating system is decisively responsible for their operational reliability. The insulating system has the task of permanently insulating electrical conductors (wires, coils, bars) from one another and from the laminated stator core or the surroundings. Outer potential control has the task of making electrical contact between the laminated stator core at ground potential and the outer side of the main insulation. This ensures that no partial discharges occur in voids in the region of the boundary layer of the insulation and the laminated core.
A distinction must be made here between                outer corona protection (OCP) for generator winding bars that have been produced by single bar production (OCP-S) and        outer corona protection (OCP) for generator winding bars that have been produced by means of the GVPI process (OCP-G).        
In the case of globally impregnated stator windings (Global Vacuum Pressure Impregnation GVPI), the entire laminated core with a fully fitted winding is impregnated and cured altogether. As a result, the adhesive bonding of the winding in the slots of the laminated core is so strong that the different coefficients of expansion of the copper, iron and insulation lead to high thermomechanical stresses between the copper, insulation and iron, which after a certain number of thermal cycles (starts and stops of the generator) may lead to tearing open of the boundary surfaces. In order to prevent the gaps from being subject to a difference in electrical potential, and the partial discharges igniting there from destroying the insulation, an outer potential control (outer corona protection, OCP) is used, in the prior art represented in FIG. 20 as a double-layered outer corona protection, such as is used for the potential control of machines processed by means of G-VPI.
An insulating base winding 70 of fine-mica tape is applied over the current-carrying Roebel bar of copper conductor elements 40, smoothing and increasing the edge radii of the thin copper conductor elements 40.
Wound thereover is a first graphite-containing conductive nonwoven tape 100, which is only connected at one point to the high-voltage potential of the copper conductor element 40 by way of a contact strip 130.
It is only thereupon that the main insulation 160 of fine-mica glass is wound. Instead of the copper conductor elements, the first conductive nonwoven tape 100 thus forms the high-voltage electrode. It is permanently adhesively bonded to the main insulation 160.
Following on top of the main insulation 160 is the inner outer corona protection winding 110 according to the prior art, an outermost separating tape 190′ and an outer outer corona protection winding 200. An outer corona protection tape 140, which is woven in the outermost separating tape 190′, connects the inner outer corona protection winding 110 and the outer outer corona protection winding 200.
The thermomechanical stresses occurring between the copper conductor assembly and the insulation during the starting and stopping of the generator may after a certain operating time lead to local detachments of the insulating sheath from the conductor, without the feared partial discharges igniting in the gaps that are produced. The region of the delamination is potential-free, because the high-voltage potential has been transferred to the conductive nonwoven tape that becomes baked fast on the main insulation. This IPC design at the highly stressed inner boundary layer between the conductor and the insulation allows turbogenerators to be operated at peak load for decades without any notable partial discharge aging.
The object of the invention is therefore to solve the aforementioned problems.
The object is achieved by an insulation system according to, with an outer corona protection according to the invention and an electrical machine according to the invention.